This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Applications 199 60 734.6, filed on Dec. 16, 1999, and 100 12 906.4, filed on Mar. 16, 2000, the entire disclosures of which are incorporated herein by reference.
The invention relates to large surface area structural components such as an aircraft doors, aircraft body sections having an outer skin reinforced by stiffening elements.
Conventionally, large surface area load carrying structural components for an aircraft are manufactured by riveting techniques and to some extent also by adhesive bonding techniques. An initially separate outer skin is riveted or adhesively bonded to a frame structure, more specifically to flanges of ribs forming the frame structure. Such structural components are, for example disclosed in German Patent Publication DE 34 38 584. Manufacturing such large surface area components is quite involved and expensive because securing the skin to the primary support frame requires setting a large number of rivets. The riveting itself requires a multitude of work steps such as drilling through the skin and through the flanges of the frame structure, setting sealing means, supplying the rivets, inserting the rivets into the drilled holes and finally setting the rivets and smoothing the outer skin surface so that the rivet heads do not increase drag.
Furthermore, a primary structural component such as an aircraft fuselage section must be capable of taking up pressure differentials between the inside of an aircraft and the outside thereof. For this purpose, stiffening elements must be provided to take up these pressure differentials. Each section, be it a door or a portion of the fuselage, must be provided with connector elements for connecting one section to the next which again increases the manufacturing effort and expense.
It is further disadvantageous that conventional frame structures, due to the materials of which the frame structures are made, and due to the required stiffening components have a high weight. Reducing such weight is an everlasting goal in aircraft construction.
In view of the above it is the aim of the invention to achieve the following objects singly or in combination:
to dimension and construct a structural large area component in such a way that it can take up the required high loads that occur in an aircraft while simultaneously reducing the weight of such structural components or at least not increasing the weight while increasing the load capacity;
to reduce the manufacturing effort and expense of such large surface area structural aircraft components;
to construct the large surface area structural component of an aircraft as an integral cast component that does not require any separate frame structures nor any riveting flanges;
to incorporate into such large surface area structural components recesses and/or housings for the installation of secondary structural elements such as windows, door handles, and other secondary structural elements;
to increase the stiffness of such large surface area components compared to the stiffness of conventional components having a skin riveted to a frame; and
to design the individual elements of the present component so that all elements can be cast simultaneously to form an integral structure in which all the elements are secured to each other as a result of the casting.
A large surface area structural component according to the invention is characterized in that a skin and reinforcing elements are integrally cast with the skin so that the reinforcing elements are rigidly secured to the skin or vice versa as a result of the casting to form an integral structure capable of taking up forces for example caused by a pressure difference on opposite sides of the structural component.
More specifically, the reinforcing elements comprise stiffening ribs that form a first grid structure integrally cast with the skin, whereby the skin closes one large surface area side of the first grid structure. The reinforcing elements further comprise stiffening walls interconnected with one another to thereby form a stiffening second grid structure. Cast junctions interconnect the second grid structure to the first grid structure opposite the skin. The skin forms for example an outer skin of an aircraft body or aircraft component such as an aircraft door. An inner skin may be secured to the second grid structure opposite the outer skin. The inner skin may also be cast with the other elements of the structure or it may be adhesively bonded to the second grid structure.
It is a particular advantage of the invention that the integrally cast structure according to the invention achieves a higher stiffness compared to conventional riveted structures capable of taking up differential pressures. Further, the casting substantially reduces the manufacturing effort and expense while simultaneously optimally reducing the weight of such structures, since riveting flanges are avoided.
Casting the outer skin together with its reinforcing stiffening first grid structure and second grid structure makes it possible to construct, for example aircraft body sections of larger size than heretofore as far as the surface area of these body sections is concerned.
By making the stiffening ribs of the first stiffening grid structure next to the skin and the stiffening walls of the second grid structure next to the stiffening ribs congruent in their cross-sectional configurations, integral casting becomes possible and the stiffness of the component is increased. By xe2x80x9ccongruentxe2x80x9d is meant in this context that a polygonal sectional configuration, parallel to the outer skin, of a grid field of the second grid structure fits onto at least one polygonal sectional configuration of a grid field of the first structure. Preferably one grid field of the second grid structure fits onto several grid fields of the first grid structure. This means that the first grid structure preferably has more grid fields than the second grid structure.
The inner skin contributes to the stiffness of the structure and if cut-outs are provided in the inner skin and/or in the stiffening walls of the second grid structure, further weight reductions are achieved.
By reinforcing the cross-section along the rims of the cut-outs, the stiffening is further improved without the need of additional stiffening components. The reinforced rims around the cut-outs require less weight than additional reinforcing elements in conventional structures which have been eliminated according to the invention.
By making the above mentioned polygonal cross-sectional configurations of the second grid structure congruent to a plurality of cross-sectional polygonal configurations of the first grid structure and the use of casting techniques becomes possible and additionally, the resulting structure is symmetrical relative to several axes such as the longitudinal aircraft axis and radial axes so that an economical production of the casting tools is possible.
The congruent sectional configurations may have any polygonal configuration, whereby even a triangular section is considered to be a polygonal configuration which also includes rectangles, squares, hexagonal configurations and any other suitable polygonal configurations. All these polygonal sectional configurations are taken as sections in a plane substantially parallel to the outer skin.
The present large surface area components are suitable for making aircraft body sections, aircraft doors, cargo bay closures, and access flaps and the like.
Due to the symmetric configuration and due to the congruent shape of the first and second grid structures it is possible to employ sand casting, high precision casting, or pressure casting for producing the present components of lightweight metals and metal alloys suitable for casting such as aluminum, magnesium and titanium and alloys thereof.